Low alloy age-hardenable steel and process

ABSTRACT

A ferrite-carbide low alloy constructional steel in the as-aged condition or capable of aging having the following composition:   Iron and impurities, balance, AND A PROCESS OF MANUFACTURE INCLUDING AGING AND TECHNIQUES FOR ROLLING THE SAME.

United States Patent 7 2] Inventor Frederick J. Semel Philadelphia, Pa.

[21] Appl. No. 785,862

[22] Filed Dec. 18, 1968 [45] Patented Nov. 9, 1971 [73] Assignee Alan Wood Stel Company Conshohocken, Pa.

Continuation-impart of application Ser. No. $49,274, Aug. 1, 1968, now abandoned. This application Dec. 18, 1968, Ser. No. 785,862

[54] LOW ALLOY AGE-HARDENABLE STEEL AND PROCESS 26 Claims, No Drawings [52] US. Cl l48/l2.3, 75/123, 75/126, 148/36 [51] lnt.Cl C2161 7/14, C22c 41/02 [50] Field of Search 75/123, 126; 148/12, 12.3, 12.4, 142, 143, 144,31, 36

[56] References Cited UNITED STATES PATENTS 2,158,651 5/1939 Becket et a1.

3,102,831 9/1963 Tisdale 75/123 X 3,328,21 l 6/1967 Nakamura. 148/12 3,472,707 10/1969 Phillips 148/36 3,494,765 2/1970 Gondo et a1. 148/36 X FOREIGN PATENTS 1,056,971 2/1967 Great Britain 75/123 1,101,193 1/1 68 Great Britain 75/123 Primary Examiner-Charles N. Lovell AttorneyWilliam Steell Jackson and Sons ABSTRACT: A ferrite-carbide ldw alloy constructional steel in the as-aged condition or capable of aging having the following composition:

Carbon 0.10% max. Manganese 0.30 to 1.50%. Silicon 0.35 max. Molybdenum 0.04 to 0.50%. Niobium 0.005 to 0.075%.

iron and impurities, balance, and a process of manufacture including aging and techniques for rolling the same.

LOW ALLOY AGE-HARDENABLE STEEL AND PROCESS DESCRIPTION OF INVENTION Carbon 0.10 percent max.,

preferably 008 percent max.

Manganese 0.30 to 1.50 percent Silicon 0.35 max.

Molybdenum 0.04 to 0.50 percent.

preferably 0.08 to 0.30 b

Niobium 0.005 to 0.075 percent Iron and impurities, balance.

A further purpose is to incorporate in a steel of very low carbon content conjoint balanced additions of niobium and molybdenum, to hot roll the steel at a finishing temperature of below l,700 F., to cool the steel inair or withwater sprays from finished rolling, to reheat the steel to an aging temperature of between l,000 and 1,200 F., and maintain it there sufficient to age the steel, and to cool the steel in air to room temperature, thus increasing the strength and maintaining high ductility by precipitating extremely fine niobium-molybdenum carbide particles.

A further purpose is to increase the yield strength from about 60,000 psi. to about 70,000 p.s.i. by theage-hardening effect.

A further purpose is to obtain a very favorable low temperature impact resistance in the age-hardened steel of the invention by the effect of the molybdenum in reducing the segregation of various constituents at the grain boundaries, such as for example, grain boundary cementite.

A further purpose is to limit the carbon content to 0.10 percent maximum, preferably 0.80 percent maximum, in order to avoid poor impact resistance at low temperatures.

A further purpose is to obtain high formability in either the as-rolled or age-hardened steel of the invention as indicated by favorable values of reduction in area.

A further purpose is to produce a low carbon steel of exceptional resistance to hydrogen embrittlement and therefore useful for the walls of pressure vessels by incorporating balanced additions of niobium and molybdenum which will combine in the steel as carbide.

A further purpose is to produce the steel of the invention according to either fully-killed practice or where compatible with alloy content, to semikilled practice.

A further purpose is to employ as a preferred range of niobium between 0.030 and 0.050 percent and as a preferred range of molybdenum between 0.08 and 0.30 percent.

A further purpose in a steel which has low carbon and agehardening properties imparted by balanced additions of niobium and molybdenum, is to further increase the yield point and retain ductility and cold formability by an addition of chromium in the range of 0. l to 0.50 percent, and preferably 020 to 0.30 percent.

A further purpose in a constructional steel containing low carbon and having age-hardening properties imparted by a balanced addition of niobium and molybdenum, is to increase the yield point while maintaining favorable ductility and cold formability by an addition of 0.005 to 0.10 percent, and preferably 0.015 to 0.070 percent of vanadium.

A further purpose in a low carbon steel having age-hardening properties by the conjoint addition of niobium and molybdenum is to further increase the yield point by controlled additions of vanadium and chromium.

A further purpose in a low carbon steel having age-hardening properties imparted by niobium and molybdenum added conjointly, is to further enhance the yield strength while retaining ductility and cold formability by adding zirconium in the range of 0.005 to 0.16 percent, and preferably in the range of 0.03 to 0.1 1 percent.

A further purpose in steel having a carbon content of 0.08 percent maximum, a niobium content of 0.005 to 0.075 percent, and preferably 0.030 to 0.040 percent and a molybdenum content of 0.08 percent to 0.50 percent, is to increase the yield strength while retaining ductility and cold formability by adding 0.0005 to 0.005 percent, and preferably 0.0015 to 0.003 percent of boron.

in one aspect of the present invention, the steel of the composition discussed above can be hot rolled at a temperature above l,700 F. (or l,750 F. depending on alloy content) and cooled in still air. In this case there is a considerable increase in yieldpoint and tensile strength and preservation of favorable ductility in the as-rolled condition, although the properties are not as good-as those obtained after aging. Another valua- 'ble property obtained in such steels in as-rolled condition is that the grain size is finer than is obtained in a comparable niobium bearing steel without the molybdenum.

Additional properties can be imparted by cooling under water sprays from hot rolling, or by cold rolling, or by both, and the as-aged properties are enhanced'thereby.

Further purposes appear in the specification and. in the claims.

In the prior art low alloy ferrite-pearlite constructional steel I has been produced according to semikilled practice having yield strengths of the order of 65,000 p.s.i. and having carbon contents of the order of 0. l 5 percent. These steels have marginal toughness as measured by low temperature impact values and low cold fonnability as measured by reduction in areas at room temperature. The addition of further alloying ingredients has been counterindicated because the experience has been that they have a detrimental effect on toughness and on cold formability.

Extensive efforts have been made to improve the yield point without disastrously affecting the toughness and cold formability by either quenching and tempering the steel or controlling the practice after finish hot rolling, for example by applying water sprays. Both of these expedients, while successful tional cold-forming properties as measured by reduction in area if the carbon content does not exceed 0.10 percent, and preferably does not extend 0.08 percent, if a balanced relation is maintained between the alloying content of niobium and the alloying content of molybdenum, and if the steel is reheated and aged at a temperature of 1,000 to l,200 F. for a time of at least 15 minutes. There is also an appreciable yield strength increase if the steel is heated up from ambient temperature and held even momentarily in the range of l,000 to 1,200 F. and then cooled.

l have discovered furthermore that additional increases in yield strength without loss in toughness as measured by low temperature impact values and without loss in cold fonnability as measured by reduction in area can be obtained by adding controlled additions of vanadium, chromium, vanadium and chromium, zirconium or boron, these additions, unlike the previous experience in steels containing 0.l5 percent carbon or thereabouts, not impairing the toughness.

I furthermore find that there are, in steels of the niobiummolybdenum base composition of the invention, unusual effects associated with the molybdenum content. For example, steel made according to the invention but not containing molybdenum will not exhibit any significant change in mechanical properties upon aging. Thus, it will be appreciated that the molybdenum plays an important part in producing in the steel the capability of being strengthened by an aging treatment. Yet, contrary to what might be expected, it has been found that once sufficient molybdenum has been added to effect a significant aging response, the further addition of molybdenum either has no effect or actually impairs to a slight extent the tensile properties obtained by aging. Furthermore, there is also an unusual effect on impact resistance. For exam ple, it is well known that increasing the molybdenum content will increase the proportion of brittle transformation product formed in the steel, such as for instance, bainite, and thus it is often noted that such a procedure results in decreased toughness at low temperatures. Yet, here again, it has been found with steels of the present invention that increasing the molybdenum very substantially improves the impact resistance and this is true for both the as-rolled and aged conditions.

The steels of the present invention have rather unusual microstructure. The principal primary phase is proeutectoid ferrite and this generally occurs in the polygonal form. The principal second phase is eutectoid carbide. Depending upon alloy content and processing conditions, the eutectoid may occur in one of three easily distinguishable forms: pearlite, intermediate product, or upper bainite. in the intermediate roduct and bainite, the ferrite constituent is acicular. Due to the low carbon content, the proportion of eutectoid is small, generally not in excess of percent by volume. A third phase, which has tentatively been identified as martensite, also occurs quite often but in very small amounts. The niobiummolybdenum carbide aging constituent is not capable of being resolved by optical microscopy.

The niobium and the molybdenum cooperate in producing a carbide age-hardening constituent and the molybdenum, presumably by its efiect on transformation characteristics, signifrcantly reduces the amount of grain boundary cementite and probably that of other grain boundary precipitates, so that strength can be increased without adverse effect on toughness as measured by low temperature impact resistance and on formability as measured by reduction in area. This is true, however, only where the carbon content does not exceed 0.10 percent, preferably 0.08 percent. At higher carbon contents, toughness and cold formability are disastrously affected by increased amount of eutectoid which is formed, whether only niobium and molybdenum are used as alloying elements, or where other additional alloying elements are employed.

It is believed that the additional elements which are beneficial to the properties when employed as alloying ingredients in addition to niobium and molybdenum function by reason of their ability to lower the A; transformation temperature of austenite. Thus they have an effect in tending to hold the niobium-molybdenum aging constituent in solution during the initial cooling from the finishing temperature of hot rolling,

which is about 1,500" to 1,700 F. The elements which have this effect are particularly chromium, vanadium, boron and zirconium, which thus aid in retaining the aging constituent in solution during the first cooling from hot rolling, increasing the potential for hardening by later heating to the aging temperature and holding at the aging temperature.

The presence of niobium and molybdenum make it possible to raise the yield point after aging to a value just short of 70,000 psi. when the steel is air cooled subsequent to rolling. lf, instead, the steel is subjected to accelerated cooling after the last pass by application of water sprays, then the presence of niobium and molybdenum make it possible to raise the yield point after aging to a value somewhat in excess of 70,000 p.s.i.

Either vanadium in the range of 0.005 percent to 0.10 percent and preferably in the range of 0.015 to 0.070 percent, or

chromium in the range of 0. l 0 to 0.50 percent and preferably from 0.20 to 0.30 percent, make it possible after aging to obtain yield points in excess of 70,000 p.s.i. without the need of water sprays after the last pass in rolling. If water sprays are used after the last rolling pass, yield points of the order of 75,000 psi. are obtained.

When both vanadium and chromium are added in the aforementioned quantities, it is then possible to obtain yield points after aging of the order of 75,000 p.s.i. without the need for accelerated cooling after rolling and yield points in excess of 75,000 p.s.i. when accelerated cooling after rolling is employed.

In all of these cases and in others to be discussed, favorable low temperature impact values are obtained and the steel is cold formable as indicated by good reductions in area.

The steel is also weldable without preheat.

in some cases it is desirable to obtain higher yield points,

and these can be secured by adding, in addition to niobium and, molybdenum, from 0.005 to 0.16 percent of zirconium, preferably from 0.03 to 0.1 1 percent of zirconium. in some cases instead of using zirconium, similar high yield points are obtained by employing boron in a concentration of 0.0005 to 0.005 percent, preferably 0.0015 to 0.003 percent with the niobium and molybdenum.

In any case, as with steels made to the niobium-molybdenum base composition and those adding vanadium or chromium or combinations thereof, alloys containing either zirconium or boron also exhibit somewhat higher yield points after aging, as for example of the order of 85,000 p.s.i., if after the last rolling pass, the steel is initially cooled in an accelerated manner by application of water sprays.

l have also discovered that the yield strength can be increased by so-called strain aging, that is, by cold rolling the steel from the as-hot rolled condition, using cold reductions up to about 30 percent, and then heating up to and holding at aging temperature. The cold working greatly enhances the aging effect.

I have furthermore discovered that by hot rolling to finishing temperatures in excess of l,700 F. (or l,750 F., depend ing on alloy content) and cooling in still air, superior properties in respect to yield point, tensile strength and fineness of grain size are obtained in the steel of the invention containing niobium and molybdenum as compared to a control containing only niobium.

The steel of the invention can be produced in the basic oxygen furnace, the open hearth fumace, the induction furnace or the electric arc furnace. While the test results given below relate primarily to steels which have been fully killed by aluminum, the principles of the invention with the exception of those relating to additions of either zirconium or boron can also be applied to steels which are semikilled.

While the greatest utility of the invention is believed to be for production of steel sheet or plate in gages of 0.050 to l inch and preferably from 0.070 to 15-inch or even 1 inch, the invention is also applicable to the production of low alloy constructional steels in the sense that they are used for building structures, machinery and the like) in the form of bars and shapes.

Because the steel of the invention has low carbon and some of the carbon is combined with molybdenum and niobium, it is believed to be especially desirable for applications requiring Y resistance to hydrogen embrittlement such as for example the walls of pressure vessels as previously mentioned.

In order to produce the aging efiect according to the invention, the steel to be aged is heated from room temperature to an aging temperature between l,000 and l,200 F and held at that temperature for a time of at least l5 minutes and still better 30 minutes. Typical aging times are one-half hour, one hour, two hours or four hours at temperature. Longer times will preferably be used for the lower temperatures. The steel of the invention is, however, quite resistant against overaging and good results have been obtained by aging at l,200 F. for 16 hours, or at 1,150 F. for hours.

While there is a pronounced increase in yield point from aging, it has been found surprisingly that the hardness, for example measured in Rockwell B, is not markedly increased by aging. However, this result may be due to the insensitivity of this particular hardness test.

In addition, the aging heat treatment also produces significant improvements in the low temperature impact resistance of the above steels and this is possibly the most unusual feature of the invention. For example, it is predictable from theory and it has been demonstrated by numerous investiga- EXAMPLE 1 Steel ingots are produced following fully-killed practice, and rolled into %-inch plate or strip width at finishing temperatures in the range of 1,500 to 1,700 F. The analyses are within the following ranges:

C 0.10 percent max. Mn 090 to 1.20 percent P 0.020 percent max.

S 0.35 percent max.

Si 0.35 percent max. Mo 0.04 to 0.50 percent Nb 0.30 to 0.050 percent.

The following table compares the tensile properties of the steel as rolled with the tensile properties as-aged according to the present invention:

TENSILE PROPERTIES As-rolled Aged Yield point, psi. 59,900 70,900 Tensile strength. p.s.i. 85,000 Elongation in 2 in., 25.0 25.0 Reduction ofarea. X 72.0 71.0

It will be evident that aging increases the yield point about 10,000 p.s.i. without any substantial effect on the elongation or reduction in area.

The following table compares the Charpy impact in footpounds between the specimens as rolled and after aging, at various testing temperatures:

It will be evident that the steel in the aged 38 -40 I3 32 60 Nil 27 condition is very tough.

EXAMPLE 2 In elaboration of the results obtained in example 1, the following is the analysis of lngot 74A which was rolled into inch plate at a finishing temperature of 1,500 to l,700 F., and subsequently cooled in still air 1 5 ,c 0.08% Mn 1 06% P 0.006% s 0.023% Si 0.030% Ni 0.00%

20 Cr 0.02% Cu 0.14% Sn 0010 Mo 0.23% Al 0.050% Ti 0.001%

25 v Nil 0 Nil Nb 0.044%

The following table gives Charpy V-notch impact properties 0 of longitudinal specimens tested at various testing tempera tures, and comparing the specimens as rolled and cooled in air to room temperature, to specimens reheated and aged at 1, 100 F. for two hours and then again cooled in still air:

Testing Temperature Impact F. Foot-pounds As rolled, air cooled Room temp. 85.5 +30 42.0 20 25.0 --40 I10 Aged 1 100 F., 2 hours, air cooled It will be evident that markedly better toughness is obtained in the aged specimens as compared with the as-rolled specimens. CHARPY IMPACT IN FOOT-POUNDS Testing It TcmperaturcF As u Aged The following table compares for plate made from lngot 74A the yield point in p.s.i., the tensile strength in p.s.i., the +30 42 68 elongation in 2 inches in percent and the reduction of area for 00 3s 42 various aging procedures:

TAB LE 1 Aging treatment 1,000 F. l,100 F. 1,200 I.

30 min. 1 hr. 2 hr. 4 hr. 30 min. 1 In. 2111'. 4 hr. 30 min. 1 hr. 2 hr. 4 In. As rolled Yield oint, p.s.i 65,000 65, 900 66,700 07, 400 60, 000 60, 500 00, 600 60, 600 68, 700 60,100 (18,700 08, 000 54,100 Tensile strength, p.s.l A 82, 600 82, 400 82, 400 82, 700 84, 800 84, 200 83, 800 84, 100 83. 800 83, 600 83, 200 82, 000 85, 1500 Elongation in 21n., perc0nt 23.0 23. 75 24. 0 23. 5 26.0 24. 0 22. 5 '11. 75 23. 25 22. 5 23. 5 0 Li. 5 Reduction of area, percent 72. 1 71. 7 70. 3 70. 6 70. 5 70.0 71.0 70.6 71.7 72. 7 7:2. 0 13. 4 70. 0

l 0.02% ofiset yield strength.

EXAMPLE 3 Cu 0.17%

Sn 0.017% In further elaboration of example 1 and example 2, lngot M 015% 748 was rolled as above described and converted into Xe-inch 4: 2,3 plate, except that instead of being entirely cooled in air the 5 v 0.001% steel was water sprayed after the last rolling pass. The analysis B was as follows: 049% c 0.08% n 106% The tensile propertles achieved as rolled and aged one hour P 00067? at l,l00 F. are shown below. These properties may be com- :2 82%;? pared with the results obtained from the product of lngot 74A Nil 5 of example 2 for similar aging conditions. The as-rolled and Cr 0.01% aged impact properties of the product of lngot 79A are shown Cu 0.14% 1 5 also. Sn 0.015% Mo 0.23% Al 0.060% Ti 0'00 1 q TENSILE PROPERTIES v Nil B Nil Nb -0 2 As rolled Aged The following table shows various mechanical properties of Yield pom, PM SW00. 7mm plate made from this lngot and aged at different temperatures Tensile strength. p.s.i. 84.200 114.300 and for different times according to the present invention. fi z l y: Notice that as compared with lngot 74A of example 2, the yield points are somewhat better for the steel of lngot 74B which was water cooled. '1 ofl'set yield strength TABLE 2 Aging treatment 1,000 F. 1,100 F. 1,200 F. AS 350 F., min 1 hr. 2 hr. 4 hr. 30 min. 1 hr. 2 hr. 4 hr. 30 min. 1 hr. 2 hr. 4 hr. rolled 30 min. Yield p01nt,p.s.i 07, 900 68.300 69,100 69, 000 70,500 70, 900 71,300 70, 000 00,500 70, 300 70, 400 71,100 1 50, 900 01, 0011 Tensile strength, p.s 83,400 85, 700 83, 200 84,000 85, 400 85,100 84, 800 82, 800 84, 200 84,800 84,100 214,000 214, 400 01,800 Elongation, percent 26.5 24. 0 26.5 22. 0 25.0 25. 25 23.0 22.0 22.0 23.75 22. 75 21.75 25.0 24.0 Reduction of area, percent 71.5 72.1 73.0 69.5 71.7 70. 5 71.1 71.3 00.7 71.0 72.8 72.3 71.7

1 0.02% ofiset yield strength.

EXAMPLE 4 4O CHARPY IMPACT IN FOOT-POUNDS Following the procedure explained in examples 1 and 2, incorporate into the ingot vanadium in the range of 0.005 to T i csllng 0.50 percent by weight, preferably 1n the range of 0.040 to Tcmpmmrcqq A ll d Aged 0.070 percent, say about 0.050 percent.

Properties comparable to those obtained in examples 1 and 74 935 2 are secured, except that the yield point is further increased :11 911 by 2,000 to 3,000 p.s.i., obtaining a reliable yield point in exi: Z cess of 70,000 p.s.i. with equal toughness and fonnability but 2 97 without the need for water sprays subsequent to rolling. if water sprays after rolling are used as in example 3, then the increase in yield point is somewhat greater, about 5,000 p.s.i.,so EXAMPLE 6 that the overall yield point of the steel approaches the 75,000 p.s.i. level.

EXAMPLE 5 Following the procedures set forth in examples 1 and 2, chromium additions are made to the ingot in the range between 0.10 and 0.50 percent by weight, preferably in the range of 0.20 to 0.30 percent, say about 0.25 percent. As with vanadium in example 4, this adds 2,000 to 3,000 p.s.i. to the yield point without water sprays after rolling or about 5,000 p.s.i. when water sprays are used, so that a reliable yield point of either 70,000 or about 75,000 is secured with otherwise equal toughness and formability.

As an instance, lngot 79A was prepared with chromium and rolled without water sprays. The resultant plate had the following analysis:

c 0.07% Mn 1 .0 1 it P 0.004% 5 0.023% 51 0.28% Ni 0.04% Cr 0.20%

The procedures of examples 1 and 2 are followed except that the ingot contains vanadium in the range referred to in example 4 and chromium in the range referred to in example 5. Here the increase in the yield point after aging over the increase obtained with the niobium-molybdenum base composition is of the order of 5,000 p.s.i. without the need for water sprays after rolling and somewhat greater than 5,000 p.s.i., usually about 7,000 p.s.i., when the water sprays are used. Thus yield points if 75,000 p.s.i. or in excess thereof are obtained with otherwise equivalent formability and impact resistance.

To illustrate this example, lngot 798 was made and rolled to -inch plate without the benefit of water sprays after the last rolling pass. The analysis of the plate was as follows:

C 0.006; Mn LOZZ' P 0.005% S 0.023% Si 0.26% Ni 0.04; CI 0.19% Cu 017% Sn (1.0 l 796 M0 0.25% Al 0.037!

V 0.050 8 Nil The tensile and impact properties of the plate-as rolled'and after aging for one hour at l, l F. were as shown.

The procedure of examples 1 and 2 is followed incorporating in the ingot 0.005 to 0.16 percent by weight, preferably 0.040 to 0.1 1 percent, say about 0.050 percent of zirconium. This has a much more pronounced effect on increasing yield point than in the case of additions of vanadium and chromium. Reliable yield points of 80,000 p.s.i. are obtained without loss in toughness or formability. When water sprays are used subsequent to rolling as in the procedure of example 3, yield points approaching 85,000 p.s.i. are obtained.

EXAMPLE 8 The procedure of examples I and 2 is followed, incorporating in the ingot 0.0005 to 0.005 percent, preferably 0.0015 to 0.003 percent by weight of boron. As with zirconium, boron has a much more pronounced effect on increasing yield point than in the case of additions of vanadium and chromium. Reliable yield points of 80,000 p.s.i. are obtained without loss in toughness or formability, without the need of water sprays after the last rolling pass, and yield points up to 85,000 p.s.i. are obtained when water sprays are used.

In further elaboration of example 8, lngot 72A was made with boron and rolled to plate without the benefit of water sprays after the last rolling pass, the plate being cooled in still air. The analysis was as follows:

M n 0.96% P 0.010% S 0.023% Si 0.29% Ni 0.06% Cr 0.02%

Cu 0. l 3% Sn' 0.0 l 4% M0 0.5 1%

Al 0.065% Ti 0.003% V Nil B 0.0022: Nb 0.037%

The following table shows various mechanical properties of the plate as rolled and aged at different temperatures and for different times according to the present invention:

EXAMPLE 9 A series of tests was carried out to demonstrate the importance of molybdenum in the base composition in producing age hardening during heat treatment subsequent to rolling. In this example lngots 65A and 653 were prepared without molybdenum but otherwise in accordance with the procedures employed in examples 1, 2 and 3. As in example 2, lngot 65A was rolled to plate without benefit of water sprays after the last rolling pass and lngot 658, as in example 3, was rolled to plate with water sprays. The analyses were as follows:

C 0.07% 0.07; Mn 1 .03 1 .00; P 0.008% 0.009% 5 0.017% 0.018% Si 0.21% 0.20; Ni 0.07% 0.021 Cr 0.02% 0.02! Cu 0. l 3' 0. 12% Sn 0.007% 0.009% M0 0.0l'ii 0.0V Al 0.059% 0.059; Ti 0.003% 0.003% V Nil Nil B 0.00039 0.0003; Nh 0.038% 0.0371

The following tables show the tensile properties as rolled and afler aging for various times and temperatures. Table 4 shows the results obtained with the product of lngot 65A, and table 5, those obtained with lngot 65B. lt is evident from these findings that no appreciable increase in yield point occurs after aging unless molybdenum is present in greater than residual concentrations.

Whereas in steels having low carbon, with molybdenum and niobium within the ranges specified, aging produces specimens whose impact values at lower testing temperatures are higher than in unaged specimens, in the case of a steel without molybdenum as in lngot 65A, the impact properties decrease after aging.

Thus for lngot 65A, the properties were as follows:

CHARPY IMPACT 1N FOOT-POUNDS The following data are offered in order to show the unusual effect of increasing the content of molybdenum in steel which is of the desired contents of carbon and niobium.

TABLE 3 Aging treatment 1,000 F. 1,100 F. 1,200 F.

r As 350 F., 30 min 1 hr. 2 hr 4 hr. 30 min. 1 hr. 2 hr. 4 hr. 30 min. 1 hr. .2 hr. 4 hr. rollcd 30 min.

Yield point, p.s.i. 72, 400 73, 200 74, 800 74, 500 76, 900 80, 200 80, 300 80, 600 800 80, 800 80, 700 79, l 59, 600 63, Tensile strength, p 88,100 90, 600 90, 600 91,000 92, 600 94, 800 J4, 200 94, 200 J3, 400 95, 000 J4, 700 13,800 89, 900 88, 600 Elongation, percent 19. 5 20. 6 19. 5 22. 5 19. 5 22. 5 21. 5 20. 5 21. 0 22. 0 '10. 75 18. 5 23. 25 25. 0 Reduction of area, percent. 73.8 72. 5 71. 6 72.6 72.3 71. 6 70. 6 72. 9 71. 9 71. 1 70.0 73. 5 71.8 72. 7

I 0.2% oflset yield strength.

I Percent best properties occur after aging, it will be evident that improvements occur in the as-rolled as well as the aged condi- 71A 71B 73A 73B 91A 91B 1on. 0.06 0.06 0. 02 0.06 0.06 0. 04 0.88 0.95 0.9 0.96 1.13 1.10 X L 0.013 0.006 0. 007 0.007 0. 003 0.004 5 E AMP E H 9 0. 53 0952 0952 09;; 0953 09;; it will be evident that the carbon content of steels of the 0.06 0.01 0.07 0. 7 0. present invention is quite critical. if the carbon content is 0.02 0.02 0.02 0. 02 0.03 0.03 0'14 Q14 0' 16 Q16 17 (L17 above 0.10 percent by weight, there is a marked lowenng of O Oig o flig g g R: 12 impact properties of the as-aged steel. particularly at lower (L656 0.658 (L653 h (1657 (L564 temperatures, and markedly better low temperature impact 0. 03 0 0 0 Ni i values are obtained if the carbon content does not exceed 0.08

N11 N11 N11 Nil Nil N11 B 0.000 0.0001 0. 0001 0. 0001 0.0002 0.0002 percefli- To lllustrate this, ingots 88A and 888 were made and rolled TABLE 4 Aging treatment 1,000 F. 1,100 F 1,200 F. As 350 1" 30 min. 1 hr. 2hr. 4 hr. 30 min 1111'. 2hr. 4 in 2111. 4 ln'. rolled 30 min. Yi ld point, p.s.i 58,100 59,500 58, 900 58,800 50,700 00,100 59,500 58,700 59, 000 53,000 59, 500 50, 500 Tensile strength, p.s.i 72,100 72. 500 71,700 71, 900 72,700 73,100 72,300 71,800 71,900 71,500 73,100 72, 300 Elongation. percent 27. 5 28.0 28.6 29. 5 24. 5 20. 0 20. 5 30. 5 29. 0 23. 0 28. 5 .25. 5 Reduction of area, ercent 75.9 76.7 76.6 77.4 76.6 76. 7 76.6 77.1 77.4 77.4 70.0 70. 2

l 0.2% ofiset yield strength.

TABLE 5 Aging treatment 1,000 F. 1,100 F. 1,200 F.

As 350 F., 30 min. 1 hr. 2hr. 4 hr. 20 min. 1 hr. 2 hr. 4 hr. 30min. 1 hr. 2111-. 4 hr. rolled 30 min. Yield point, .s.i 59,500 59, 700 59,900 59,200 60,900 00,700 00,200 59,000 60,000 00,100 59,700 50, 400 00,000 60,100 Tensile strength, p.s 73,200 72,300 72,100 72,600 73,400 73, 600 72,800 72, 400 72, 200 73,600 72,300 71,400 73,300 72,300 Elongation, percent- 25.5 25.0 29.5 20. 75 29. 75 28.25 28.0 20.75 31.5 25. 20.0 29. 75 20.0 30.0 Reduction of area, per 75.2 76.4 75.4 75.1 75.4 76.0 76.5 76. 5 77.1 76.11 80.0 77.3 75. 0 76. 6

0.2% ofiset yield strength.

TABLE 6.MECHANICAL PROPERTIES AS ROLLED AND AGED AT 1,100" F. FOR TWO HOURS ingot 71A 71A 71B 71B 73A 73A 73B 73B 91A 01A 91B 918 Condition As As As As As As rolled Aged rolled Aged rolled Aged rolled Aged rolled Aged rolled Aged Yield point, p.s.i 53, 000 69,100 54,900 68, 000 52,900 68, 500 00,600 70,100 60,000 68,630 60,000 72,410 Tensile strength, p.s.i 80,600 81,800 81,400 82, 400 80,000 80,400 82,300 81,200 83, 730 82,840 82,500 82,590 Elong. in 2in., percent 27.5 25.0 25.5 24.6 25.5 22.0 27.5 22.0 20.0 18.6 26.6 27.6 Reduction of area, percent 74. 8 72. 5 73. 1 73. 3 73. 3 73. 7 73.0 76. 4 72. 8 13.2 58. 2 63.0

1 Values relating to the as-rolled condition are 0.2 otfset yield strength.

The ingots bearing A designations were cooled in still air into 50-inch plates having compositionsas shown below. from the last pass of hot rolling, and those designated B were 50 cooled in water sprays from said last pass. CHEMICAL ANALYSIS The tensile properties corresponding to the as-rolled and aged conditions are shown in table 6 and the impact properties for these two conditions of steels from ingots having A Inga, 88A 88B des1gnat1ons are shown below. In all cases, agmg was at 1,100 55 c 0.10; 0.14% F. for two hours. Mn

P 0.004 0.004 5 0.024 0.022 Char m act '110otounds Si W l p u p Ni 0.04 0.04 Testing Ingot 71A Ingot 73A Ingot 01A 60 Cr 0.03 0.03 temperature, 0,16 016 F. As-rolled Aged As r0l1ed Aged As-rolled Aged Sn (HHS 104 134 65 105 60 75 30 95 26 76 Al 0.052 0.040 28 g0 80 25 1 7 21 '11 Nil Nil 4 7 48 a 2 B 0.0010 0.0016 19 46 20 12 Nb mm 0.0

l imperfection in specimen.

A careful examination of the tensile data will reveal, as indicated earlier, that the as-aged yield points are definitely not it is to be noted that ingot 88A has an intermediate content improved and, in fact, in some cases, tend to decrease slightly of molybdenum (0.23 percent) and ingot 88B has a relatively as the molybdenum content is increased. On the other hand, as also mentioned earlier, the above data show that that the impact resistance of the steel is very substantially improved by increasing the molybdenum, and although these findings are consistent with the results of previous examples in that the high molybdenum content (0.46 percent), and that in both cases, the carbon contents are high in the present context, being respectively 0.16 percent and 0. l4 percent.

The impact properties of these steels in both the as-rolled and aged conditions are shown below.

CHARPY V NOTCH IMPACT VALUES FROM LON GI- 8 3" 7o TUDINAL SPECIMENS AS AGED AT 1,100 F. FOR ONE HOUR c 0.057 0.055 I t t 83A 88B Mn 0.84 0.77

ngo con 1 mm es mg P 0005 0007 Temperature, F. As rolled Aged As rolled Aged S 0'0") 002: Room temperature 28 10 23 16 5 5i 0 12 7.5 5.5 5.0 Ni 0.02 0.01 20 6. 5 9.0 5. 5 5.0 Cr 0.03 0.02 7 Cu 0.10 0.01; It is very obvious from these data that increasing the carbon 0 3' 3?? 332 has adversely affected the impact resistanceJMoreover, there M 0,060 are very clear indications in these findings to the effect that Nb 52 0.051 the increased carbon has completely altered the metallurgical character of the steel. For example, comparison of the room temperature impact values shows quite wellthat the toughness 15 The ingots were rolled into plate of thicknesses of 1 inch, tends to decrease after ag g. rather than increase. More three-fourths inch, one-half inch and three-eighth inch at Clear. p aps i he d itional fact that these findings show an finishing temperatures listed, to obtain properties as-rolled opposite trend when compared with results of the previous exfollowed by cooling in still air as set forth in table 7. ample. Instead of improving impact resistance, the increased Specimens from each plate were also aged at l, 1 50 F. for one molybdenum content of lngot 888 over lngot 88A has aphour, and cooled in still air. parently resulted in a decrease in toughness in both the asit will be noted that lngot Series according to the present rolled and aged conditions. invention gave a considerable improvement in yield point and TABLE 7 1 inch plate inch plate Yield Tensile Elongation Reduction Yield Tcnslle Elongation Reduction Finishing point, strength, in 2", of area, Finishing point, strength, in 2 of 011 11, Ingot series temp., F p.s.i. p.s.i. percent percent temp, F. 05.1 psi pen-cut Ingot 30 as 1'0lled 1,000 to 1,050 .i 51, 670 71,300 28. 5 68. 5 000 to 1 590 157,160 76, 300 00. 0 5%, 670 71, 640 20.5 60. 0 I -1g7, 160 76, 30 00. In 0t 30 as a ed 1,000 to 1,950 .15 ,170 72,800 27.5 68.0 0,660 77, 0 0.

g g 55,420 72,890 28.0 68.5 1 -i511, 660 77,130 60.0 Ingot 70 as rolled 1,000 to 1,500-. 50,670 68,150 20.0 68.0 900,01 500 54, 420 70,800 67.5 50, 670 67, 000 30.0 68.0 Y 154, 420 70, 800 68. 0 Ingot 70 as aged... 1,000 to 1,960 51, 670 68, 400 28. 5 68. 5 1,000 to 1,950- .55, 890 71,680 138. 0

inch plate 30 inch platc In at 30 as rolled 1,850 to1,900-. 56,770 72,810 24.0 72.0 64, 730 78,160 10.5 72.0 g 55, 840 73, 130 24. 5 72. 3 i 030 77, 060 10. 0 72. 5 Ingot 30 as aged 1,850 to 1,000. 57, 740 73, 330 23. 5 71. 3 1 750 t 1 800 164, 330 78, 360 16. 0 72. 0 58,170 73, 210 23. 5 72. 0 1 1 0 [64, 870 78, 240 1a. 5 73.1 I11got70 as roll0d 1,350 to 1,000-. 54,150 68, 730 25. 0 71.6 750 w 1 800 57, 330 70,220 15. 5 72.4 54,150 68,820 24.0 71.6 J 56,010 70,540 21.5 71.3 Ingot 75 as aged 1,850 to 1,000- '54, 050 60,130 24. 5 71.0 1,750 to 1,800. 56, 510 78, 540 21. 0 72. 0

EXAMPLE l2 tensile strength in the as-roll'ed condition, as compared to the The procedure of examples I, 2 and 3 is carried out except that after completion of hot rolling, the steel is cold reduced about 15 percent. After reheating to aging temperature and then slowly cooling to room temperature, in still air, it is found that the yield point is increased beyond what would be obtained in the absence of cold working by about l0,000 to 15,000 p.s.i. This is true in all of the steel compositions of the present invention, those including molybdenum and niobium, and also those adding vanadium or chromium or chromium and vanadium, or zirconium or boron.

The best properties as-aged will be obtained by finishing at a temperature below l,700 F. (or 1,750 F. depending on alloy content) and then cooling as rapidly as convenient, as for example, by water sprays short of quenching, and then aging as above described.

Some of the benefit from improved properties by aging can be obtained, however, by changing the finishing conditions from those discussed above, and improved properties which are a compromise (not as good as those obtained by subsequent aging) can be obtained in the hot rolled condition by this technique.

To achieve this, it is necessary to finish at a temperature above l,700 F. (or l,750 F. depending on alloy content), and cool in still air. Thus beneficial properties were obtained by finishing at various temperatures up to l,900 or l,950 F. It will be understood that in usual noncontinuous mill rolling practice the finishing temperature for the lighter gages is likely to be on the lower side and for the heavier gages on the higher side.

A series of ingots was hot rolled having the following analyses on the average:

control, ingot Series 70, especially in the lighter" gages. This is equally true of steels adding chromium, vanadium, chromium and vanadium, zirconium or boron as above described.

I have also found that the addition of molybdenum to niobium containing steel of the invention has a significant effect in improving the grain size in the as-rolled condition. Molybdenum seems to have a beneficial effect over a wide range of finishing conditions.

These findings are illustrated in the following data:

As-rollcd grain size in invcrsc Finishing sun-.111 root of Plato temperature 1111-011 grain guruin in 1%, cooled di nnvli-r ln ingot series inches in still air 1n1llnn1tc1's h 1, Hill) 1,5150 7. 00

5 l, T50 l, 500 9. 5'3

Thus the samples of steel according to the invention are of significantly finer grain size than the control omitting the molybdenum. The numbers above approximate ASTM grain size numbers. I I

While the above examples illustrate properties obtained in sheet and plate products, these properties are also illustrative of properties which are secured in other low alloy constructional steel fonns, such as bars and shapes.

it will be evident that the principles of the invention can be applied where desired by selling a steel according to the invention in the as-rolled condition and then aging after fabrication or aging in connection with a stress relief anneal after welding during fabrication.

It will be evident that in the case of compositions of alloys, the percentages are by weight.

In view of my invention and disclosure, variations and modifications to meet individual whim or particular need will doubtless become evident to others skilled in the art to obtain all or part of the benefits of my invention without copying the composition and process shown, and I, therefore, claim all such insofar as they fall within the reasonable spirit and scope of my claims.

We claim:

1. A ferrite-carbide low alloy constructional steel in the hot rolled, cooled without quenching, and directly aged condition having the following composition by weight:

carbon 010% max. silicon 0.35% max.

manganese 0.30 to L50)? niobium 0.005 to 0.075% molybdenum 0.04 to 0.50

iron and impurities, balance.

2. A steel of claim 1, having the following composition by weight in the following respect:

carbon 0.08% max.

rolled, cooled without quenching, and directly aged condition having the following composition by weight:

carbon 0.l% max silicon 0.35% max. manganese 0.30 to l.50% niobium 0.005 to 0.075% molybdenum 0.04 to 0.50% vanadium up to 0.l0% chromium up to 0.050% zirconium up to 0. l 6% iron and impurities. balance.

6. A steel of claim 5, having the following composition by weight in the following respect:

carbon 0.08% max.

7. A steel of claim 6, having the following composition by weight in the following respect:

molybdenum 0.08 to 0.30%.

8. A steel of claim 5, having the following composition by weight in the following respect:

niobium 0.03010 0.05076.

9. A ferrite-carbide low alloy constructional steel in the hot rolled, cooled without quenching, and directly aged condition having the following composition by weight:

carbon 0.08% max. silicon 0.35% max. manganese 0.30 to 1.50% niobium 0.005 to 0.075% molybdenum 0.04 to 0.50%

boron 0.0005 to 0.005% iron and impurities. balance.

hot rolled, cooled without quenching, and directly aged condition having the following composition by weight:

carbon 0.08% max.

silicon 0.35% max. manganese 0.30 to l.50% niobium 0.005 to 0.075% molybdenum 0.04 to 0.50% boron 0.0005 to 0.005% vanadium up to 0. l0% chromium up in 0.50% zirconium up to 0. l 6% iron and impurities. balance.

12. A ferrite-carbide low alloy constructional steel in the hot rolled, cooled in air, and directly aged condition having the following composition by weight:

carbon 0.10% max. silicon 0.35% max.

manganese 0.30 to l.50% niobium 0.005 to 0.075% molybdenum 0.04to 0.50% vanadium up to 0. l0! chromium up to 0.50% zirconium up to OJbX iron and impurities balance.

carbon 010% max. silicon 0.35% max.

manganese 0.30 to L50! niobium 0.005 to 0.075% molybdenum 0.04 to 0.50;

iron and impurities. balance.

directly cooling the steel to room temperature without quenching, without austenitizing, reheating the steel to a temperature of l,000 to l,200 F. and holding it at that temperature to age it, and cooling the steel in air to room temperature.

15. A process of claim 14, in which the steel has the following composition by weight in the following respect:

carbon 0.08% max.

16. A process of claim 14, in which the steel has the following composition by weight in the following respect:

molybdenum 0.08 to 0.30;

structional steel, which comprises hot rolling a steel having the following composition by weight:

carbon (LIO'Z max silicon 0.35 max manganese 0.30 to I 50' niobium 0.005 100.075;

molybdenum 0.04 to 0.50% vanadium up to 0.10% chromium up to 0.50% zirconium up to 0.16%

iron and impurities, balance. cooling the steel to room temperature, without austenitizing reheating the steel to a temperature of l,000 to 1,200 F. and holding it at that temperature to age it, and cooling the steel in air to room temperature.

19. A process of claim 18, in which the steel has the following composition by weight in the following respect:

carbon 0.08% max.

20. A process of claim 18, in which the steel has the following composition by weight in the following respect:

molybdenum 0.08 to 0.30%.

21. A process of claim 18, in which the steel has the following composition by weight in the following respect:

niobium 0.03010 0.050%.

22. A process of making ferrite-carbide low alloy construc- 525 tional steel which comprises hot rolling a steel having the following composition by weight:

carbon 0.08% max. 3

silicon 0.35% max. 1

manganese 0.30 to l.50%

niobium 0.05 to 0.75%

molybdenum 0.04 to 0.50%

boron 0.0005 to 0.005%

iron and impurities. balance,

directly cooling the steel to room temperature without quenching, without austenitizing reheating the steel to a temperature of l,000 to 1,200 F. and holding it at that temperature to age it, and cooling the steel in air to room temperature.

23. A process of claim 22, in which the steel has the foilow- 40 ing composition by weight in the following respect:

boron 0.015 to 0.003%.

24. A process of making a ferrite-carbide low alloy constructional steel, which comprises hot rolling a steel having the following composition by weight:

boron 0.0005 to 0.005% vanadium up to 0. I056 chromium up to 0.50% zirconium up to 0. I61

iron and impurities, balance.

directly cooling the steel to room temperature without quenching, without austenitizing reheating the steel to a temperature of l,000 to 1,200 F. and holding it at that temperature to age it, and cooling the steel in air to room temperature.

carbon 0.10% max. silicon 0.35% max. manganese 0.30 to l.5 0% niobium 0.005 to 0.057% molybdenum 0.04 to 0.50% vanadium up to 0. I0% chromium up to 0.50% zirconium up to 0.16%

iron and impurities, balance.

25. A process of making a ferrite-carbide low alloy constructional steel, which hot rolling a steel having the following composition by weight:

carbon 0.10% max. silicon 0.35% max. manganese 0.30 to L501: niobium 0.005 to 0.075% molybdenum 0.04 to 0.50% vanadium up to 0.10% chromium up to 0.50% zirconium up to 0.16%

iron and impurities, balance.

directly cooling the steel in air to room temperature, without austenitizing reheating the steel to a temperature of 1,000 to 1,200 F. and holding it at that temperature to age it, and cooling the steel in the air to room temperature.

26. A process of making a ferrite-carbide low alloy constructional steel, which comprises hot rolling a steel having the following composition by weight:

carbon 0.l0% max.

silicon 0.35% max. manganese 0.30 to 1.50% niobium 0.005 to 0.75% molybdenum 0.04 to 0.50% vanadium up to 0.10% chromium up to 0.50% zirconium up to 0.16%

iron and impurities, balance.

directly cooling the steel to room temperature with the aid of a water spray short of quenching, without austenitizing reheating the steel to a temperature of 1,00020 to 1,200dr F. and holding it at the temperature to age it, and cooling the steel in air to room temperature.

l ll 0 t I! Frederick J. Semel Column 1, line 8, change the word "age-handenable" to --ag;e-hardemable- Column 1, line 11, the word "as" should be --in--.

, change "0.80" to --0.08--. T

, change word "extend" to --exceed--.

--the-- after "with" Column 1, line 4 Column 2, line 5 Column 3, line 21, insert the word and before "steele".

Column 4, line 13, insert the word --the--- after "in" and before "others".

line 46, the word "oxygen" should not be hyphenated;

line 32, change "0.35" percent mex. to percent max.

line 34, change "0.30" to --0.030-- line 44, in the Table entitle "TEN-SILK PROPERTIES column entitled "As-rolled" ogpoeite "Tensile 12.5 .i-. insert the numeral 4,400--.

Column 4,

Column 5, -0.035-- Column 5,

Column 5, under the strength,

Column 6, line 18, the numeral opposite "81" which is "0.030%" should be "0.30%".

Column 6, line 45 under the heading "Aged llOO'F.,

2 hours, air cooled" the numeral "30" ehoulo be --+30--. Column 6, line 57, the word "it should be removed.

under the heading "1 hr. opposite the period in 68.300" should Column 7, Table 2, "Yield point, 19.8 .i. be changed to a coma as follows:

A -,.l. n n Q Patent are heresy ceumenl. 3.. shown selow.

Column 8, line 27, in the table "TENSILE PROPERTIES" the words offset yield strength" should follow the number Y *0.2" as follows: --*0.2% offset yield strength--.

Column 8, line 45, in the Table "CHARPY IMPACT IN FOOT- POUNDS under the heading "Testing Temperature F.

the numeral --75-- should be inserted after the and in line 46 under the heading "Testing Temperature F. --0-- should be placed in this column.

Column 8, line 61, the word "if" before "75,000" should be changed to --ef--.

Column 8, line 67, opposite the letter "C" the numeral "0.006%" should be changed to --0.o6%--.

Column 9, line 15, the numeral '*0.02l'" should be changed to -*0.2-- and the words "at offset yield strength" should follow the number "*0.2" as follows:

--*0.25$ offset yield strength.

Column 9, line in the table I'CHARPY IMPACT IN FOOT- POUNDS" under the heading "Testing Temperature F. after the the numeral --60-- should be inserted.

Column 10, line 50, after the Table "CHARPY IMPACT IN FOOT-POUNDS and before "Example 10'' Tables 4 and 5 should be positioned.

Column 12, in Table 5, under the heading "As rolled" the footnote --l-- should be inserted before or after the numeral "60,900".

PC4050 UNITED STATES PATENT oTFTcs CERTEFICATE OF CORRECTION Patent No. 3: 9, 3 3 Dated NQV 9, 1.971

inventor(s) Frederick J. Semel It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column 11, line 55, the Table 6 should be positioned here before the table "Charpy Impact in foot-pounds Column 11, line 72, remove the second word "that".

Columns 13 and i l, Table 7, under the heading '"1 inch plate" "Finishing temp., F. opposite "ingot 70 as rolled" the numbers "1,900 to 1,500" should be --1,900 to 1,950--.

Columns 13 and 1 4, Table 7, under the heading "3/4 inch plate" under the heading "Finishing temp., F. opposite the words "ingot 30 as rolled" the numbers "1,900 to 1,590"

should be --l,900 to 1,950--.

Columns 13 and 14, Table '7, under the heading "3/4 inch plate" "Finishing temp., F. opposite "ingot 70 as rolled" the numbers "1,900 to 1,500" should be --1,900 to 1,950

Columns 13 and 14, Table 7, after the first heading of Reduction of area, percent" there should be no column of brackets but instead a space.

Column 15, line 13, change "We" to --i--.

Column 16, line 38, following the words "composition by weight: the table of compounds in column 18, line 10 starting with "carbon 0.10% max. should be moved.

in that table, column 18, line 13, the value for "niobium" is "0.005 to 0.057%" and should be 0.005 to 0.075%.

Column 17 line 6 before "cooling" insert directly J same line 6, after "temperature," insert without quenching,

mm: R 3,619,303 Dated Nov. 94 1971 Inventorb) Frederick IQl I: is certified that error appears in the above-identified patent "aid Lctt- 5 Patent are hereby corrected as shown below:

3.. bun D e Column 17, line 52, the value for "niobium" is "0.005 to 0.0075%"&aheu1d be as follows: --o.oo5 t0 0.075%.

Column 18 line 19, after the word "which" and befere the word het" insert the word --comprises--.

Column 18, line 3 after the word "in" and before the word "air" remove the word "the".

Celumn 18, line 41, the value for "niobium" 1s "0.005 to 0.75%" and should be --0.005 to 0.075%.

Column 18, line 49 the phrase "of 1,00020 to l,200dr F. is wrong and eheuld be changed to --of 1000' to l200F.--.

Signed and sealed this 26th day of September 1972.

(SEAL) Attest:

EDWARD M.FLETCHER,JR. ROBERT GOTTSCHALK Attesting Officer Commissioner of Patents 

2. A steel of claim 1, having the following composition by weight in the following respect: carbon 0.08% max.
 3. A steel of claim 2, having the following composition by weight in the following respect: molybdenum 0.08 to 0.30%.
 4. A steel of claim 1, having the following composition by weight in the following respecT: niobium 0.030 to 0.050%.
 5. A ferrite-carbide low alloy constructional steel in the hot rolled, cooled without quenching, and directly aged condition having the following composition by weight: carbon 0.10% max silicon 0.35% max. manganese 0.30 to 1.50% niobium 0.005 to 0.075% molybdenum 0.04 to 0.50% vanadium up to 0.10% chromium up to 0.050% zirconium up to 0.16% iron and impurities, balance.
 6. A steel of claim 5, having the following composition by weight in the following respect: carbon 0.08% max.
 7. A steel of claim 6, having the following composition by weight in the following respect: molybdenum 0.08 to 0.30%.
 8. A steel of claim 5, having the following composition by weight in the following respect: niobium 0.030 to 0.050%.
 9. A ferrite-carbide low alloy constructional steel in the hot rolled, cooled without quenching, and directly aged condition having the following composition by weight: carbon 0.08% max. silicon 0.35% max. manganese 0.30 to 1.50% niobium 0.005 to 0.075% molybdenum 0.04 to 0.50% boron 0.0005 to 0.005% iron and impurities, balance.
 10. A steel of claim 9, having the following composition by weight in the following respect: boron 0.0015 to 0.003%.
 11. A ferrite-carbide low alloy constructional steel in the hot rolled, cooled without quenching, and directly aged condition having the following composition by weight: carbon 0.08% max. silicon 0.35% max. manganese 0.30 to 1.50% niobium 0.005 to 0.075% molybdenum 0.04 to 0.50% boron 0.0005 % to 0.005% vanadium up to 0.10% chromium up to 0.50% zirconium up to 0.16% iron and impurities, balance.
 12. A ferrite-carbide low alloy constructional steel in the hot rolled, cooled in air, and directly aged condition having the following composition by weight: carbon 0.10% max. silicon 0.35% max. manganese 0.30 to 1.50% niobium 0.005 to 0.075% molybdenum 0.04to 0.50% vanadium up to 0.10% chromium up to 0.50% zirconium up to 0.16% iron and impurities balance.
 13. A ferrite-carbide low alloy constructional steel in the hot rolled, cooled with the aid of a water spray short of quenching, and directly aged condition having the following composition by weight: carbon 0.10% max. silicon 0.35% max. manganese 0.30 to 1.50% niobium 0.005 to 0.075% molybdenum 0.04 to 0.50% vanadium up to 0.10% chromium up to 0.50% zirconium up to 0.16% iron and impurities, balance.
 14. A process of making a ferrite-carbide low alloy constructional steel, which comprises hot rolling a steel having the following composition by weight: carbon 0.10% max. silicon 0.35% max. manganese 0.30 to 1.50% niobium 0.005 to 0.075% molybdenum 0.04 to 0.50% iron and impurities, balance, directly cooling the steel to room temperature without quenching, without austenitizing, reheating the steel to a temperature of 1,000* to 1,200* F. and holding it at that temperature to age it, and cooling the steel in air to room temperature.
 15. A process of claim 14, in which the steel has the following composition by weight in the following respect: carbon 0.08% max.
 16. A process of claim 14, in which the steel has the following composition by weight in the following respect: molybdenum 0.08 to 0.30%.
 17. A process of claim 14, in which the steel has the following composition by weight in the following respect: niobium 0.030 to 0.050%.
 18. A process of making a ferrite-carbide low alloy constructional steel, which comprises hot rolling a steel having the following composition by weight: carbon 0.10% max. silicon 0.35% max. manganese 0.30 to 1.50% niobium 0.005 to 0.075% molybdenum 0.04 to 0.50% vanadium up to 0.10% chromium up to 0.50% zirconium up to 0.16% iron and impurities, balance, cooling the steel to room temperature, without austenitizing reheating the steel to a temperature of 1,000* to 1,200* F. and holding it at that temperature to age it, and cooling the steel in air to room temperature.
 19. A process of claim 18, in which the steel has the following composition by weight in the following respect: carbon 0.08% max.
 20. A process of claim 18, in which the steel has the following composition by weight in the following respect: molybdenum 0.08 to 0.30%.
 21. A process of claim 18, in which the steel has the following composition by weight in the following respect: niobium 0.030 to 0.050%.
 22. A process of making ferrite-carbide low alloy constructional steel which comprises hot rolling a steel having the following composition by weight: carbon 0.08% max. silicon 0.35% max. manganese 0.30 to 1.50% niobium 0.05 to 0.75% molybdenum 0.04 to 0.50% boron 0.0005 to 0.005% iron and impurities, balance, directly cooling the steel to room temperature without quenching, without austenitizing reheating the steel to a temperature of 1,000* to 1,200* F. and holding it at that temperature to age it, and cooling the steel in air to room temperature.
 23. A process of claim 22, in which the steel has the following composition by weight in the following respect: boron 0.015 to 0.003%.
 24. A process of making a ferrite-carbide low alloy constructional steel, which comprises hot rolling a steel having the following composition by weight: carbon 0.08% max. silicon 0.35% max. manganese 0.30to 1.50% niobium 0.005 to 0.0075% molybdenum 0.04 to 0.50% boron 0.0005 to 0.005% vanadium up to 0.10% chromium up to 0.50% zirconium up to 0.16% iron and impurities, balance, directly cooling the steel to room temperature without quenching, without austenitizing reheating the steel to a temperature of 1,000* to 1,200* F. and holding it at that temperature to age it, and cooling the steel in air to room temperature.
 25. A process of making a ferrite-carbide low alloy constructional steel, which hot rolling a steel having the following composition by weight: carbon 0.10% max. silicon 0.35% max. manganese 0.30 to 1.50% niobium 0.005 to 0.075% molybdenum 0.04 to 0.50% vanadium up to 0.10% chromium up to 0.50% zirconium up to 0.16% iron and impurities, balance, directly cooling the steel in air to room temperature, without austenitizing reheating the steel to a temperature of 1,000* to 1,200* F. and holding it at that temperature to age it, and cooling the steel in the air to room temperature.
 26. A process of making a ferrite-carbide low alloy constructional steel, which comprises hot rolling a steel having the following composition by weight: carbon 0.10% max. silicon 0.35% max. manganese 0.30 to 1.50% niobium 0.005 to 0.75% molybdenum 0.04 to 0.50% vanadium up to 0.10% chromium up to 0.50% zirconium up to 0.16% iron and impurities, balance, directly cooling the steel to room temperature with the aid of a water spray short of quenching, without austenitizing reheating the steel to a temperature of 1,00020 to 1,200*dr F. and holding it at the temperature to age it, and cooling the steel in air to room temperature. 